This question is designed to be a comprehensive question about "cannot find symbol" compilation errors in Java.

10 comments

@BlaCk HoLe 2018-08-29 08:22:50

You can also get this error if you're forgot a new as in:

int i = Integer(); ---->> should be "new Integer()"

(This is why I get the error in my case)

@LuCio 2018-08-30 14:42:11

Do you mean that declaring a variable Boolean b; instead of boolean b; can cause this error? And to which type string are you referring to?

@BlaCk HoLe 2018-08-31 08:09:16

Yes in my case, I had the same error, and when I changed the variable declaration Boolean b; to boolean b; it works

@Stephen C 2018-10-31 01:39:02

This is misleading. Simply using Boolean instead of boolean or Integer instead of int will not cause this error. You need to do something else as well. Both Boolean and Integer are valid type names, and will be understood by the Java compiler.

@BlaCk HoLe 2018-10-31 14:57:10

You are right @StephenC

@Stephen C 2018-10-31 22:21:49

Your example is a dup. Search this Q&A page for "should be 'new String()'" ...

@Stephen C 2014-09-07 01:12:08

1. What does a "Cannot find symbol" error mean?

Firstly, it is a compilation error1. It means that either there is a problem in your Java source code, or there is a problem in the way that you are compiling it.

Your Java source code consists of the following things:

Keywords: like true, false, class, while, and so on.

Literals: like 42 and 'X' and "Hi mum!".

Operators and other non-alphanumeric tokens: like +, =, {, and so on.

Identifiers: like Reader, i, toString, processEquibalancedElephants, and so on.

Comments and whitespace.

A "Cannot find symbol" error is about the identifiers. When your code is compiled, the compiler needs to work out what each and every identifier in your code means.

A "Cannot find symbol" error means that the compiler cannot do this. Your code appears to be referring to something that the compiler doesn't understand.

2. What can cause a "Cannot find symbol" error?

As a first order, there is only one cause. The compiler looked in all of the places where the identifier should be defined, and it couldn't find the definition. This could be caused by a number of things. The common ones are as follows:

For identifiers in general:

Perhaps you spelled the name incorrectly; i.e. StringBiulder instead of StringBuilder. Java cannot and will not attempt to compensate for bad spelling or typing errors.

Perhaps you used underscores inappropriately; i.e. mystring and my_string are different. (If you stick to the Java style rules, you will be largely protected from this mistake ...)

Perhaps you are trying to use something that was declared "somewhere else"; i.e. in a different context to where you have implicitly told the compiler to look. (A different class? A different scope? A different package? A different code-base?)

For identifiers that should refer to variables:

Perhaps you forgot to declare the variable.

Perhaps the variable declaration is out of scope at the point you tried to use it. (See example below)

For identifiers that should be method or field names:

Perhaps you are trying to refer to an inherited method or field that wasn't declared in the parent / ancestor classes or interfaces.

Perhaps you are trying to refer to a method or field that does not exist (i.e. has not been declared) in the type you are using; e.g. "someString".push()2.

Perhaps you are trying to use a method as a field, or vice versa; e.g. "someString".length or someArray.length().

For identifiers that should be class names:

Perhaps you forgot to import the class.

Perhaps you used "star" imports, but the class isn't defined in any of the packages that you imported.

Perhaps you forgot a new as in:

String s = String(); // should be 'new String()'

For cases where type or instance doesn't appear to have the member you were expecting it to have:

Perhaps you have declared a nested class or a generic parameter that shadows the type you were meaning to use.

Perhaps you are shadowing a static or instance variable.

Perhaps you imported the wrong type; e.g. due to IDE completion or auto-correction.

Perhaps you are using (compiling against) the wrong version of an API.

Perhaps you forgot to cast your object to an appropriate subclass.

The problem is often a combination of the above. For example, maybe you "star" imported java.io.* and then tried to use the Files class ... which is in java.nio not java.io. Or maybe you meant to write File ... which is a class in java.io.

Here is an example of how incorrect variable scoping can lead to a "Cannot find symbol" error:

This will give a "Cannot find symbol" error for i in the if statement. Though we previously declared i, that declaration is only in scope for the for statement and its body. The reference to i in the if statement cannot see that declaration of i. It is out of scope.

(An appropriate correction here might be to move the if statement inside the loop, or to declare i before the start of the loop.)

Here is an example that causes puzzlement where a typo leads to a seemingly inexplicable "Cannot find symbol" error:

for (int i = 0; i < 100; i++); {
System.out.println("i is " + i);
}

This will give you a compilation error in the println call saying that i cannot be found. But (I hear you say) I did declare it!

The problem is the sneaky semicolon ( ; ) before the {. The Java language syntax defines a semicolon in that context to be an empty statement. The empty statement then becomes the body of the for loop. So that code actually means this:

for (int i = 0; i < 100; i++);
// The previous and following are separate statements!!
{
System.out.println("i is " + i);
}

The { ... } block is NOT the body of the for loop, and therefore the previous declaration of i in the for statement is out of scope in the block.

Here is another example of "Cannot find symbol" error that is caused by a typo.

int tmp = ...
int res = tmp(a + b);

Despite the previous declaration, the tmp in the tmp(...) expression is erroneous. The compiler will look for a method called tmp, and won't find one. The previously declared tmp is in the namespace for variables, not the namespace for methods.

In the example I came across, the programmer had actually left out an operator. What he meant to write was this:

int res = tmp * (a + b);

There is another reason why the compiler might not find a symbol if you are compiling from the command line. You might simply have forgotten to compile or recompile some other class. For example, if you have classes Foo and Bar where Foo uses Bar. If you have never compiled Bar and you run javac Foo.java, you are liable to find that the compiler can't find the symbol Bar. The simple answer is to compile Foo and Bar together; e.g. javac Foo.java Bar.java or javac *.java. Or better still use a Java build tool; e.g. Ant, Maven, Gradle and so on.

There are some other more obscure causes too ... which I will deal with below.

3. How do I fix these errors ?

Generally speaking, you start out by figuring out what caused the compilation error.

Look at the line in the file indicated by the compilation error message.

Identify which symbol that the error message is talking about.

Figure out why the compiler is saying that it cannot find the symbol; see above!

Then you think about what your code is supposed to be saying. Then finally you work out what correction you need to make to your source code to do what you want.

Note that not every "correction" is correct. Consider this:

for (int i = 1; i < 10; i++) {
for (j = 1; j < 10; j++) {
...
}
}

Suppose that the compiler says "Cannot find symbol" for j. There are many ways I could "fix" that:

I could change the inner for to for (int j = 1; j < 10; j++) - probably correct.

I could add a declaration for jbefore the inner for loop, or the outer for loop - possibly correct.

I could change j to i in the inner for loop - probably wrong!

and so on.

The point is that you need to understand what your code is trying to do in order to find the right fix.

4. Obscure causes

Here are a couple of cases where the "Cannot find symbol" is seemingly inexplicable ... until you look closer.

Incorrect dependencies: If you are using an IDE or a build tool that manages the build path and project dependencies, you may have made a mistake with the dependencies; e.g. left out a dependency, or selected the wrong version. If you are using a build tool (Ant, Maven, Gradle, etc), check the project's build file. If you are using an IDE, check the project's build path configuration.

You are not recompiling: It sometimes happens that new Java programmers don't understand how the Java tool chain works, or haven't implemented a repeatable "build process"; e.g. using an IDE, Ant, Maven, Gradle and so on. In such a situation, the programmer can end up chasing his tail looking for an illusory error that is actually caused by not recompiling the code properly, and the like ...

An earlier build problem: It is possible that an earlier build failed in a way that gave a JAR file with missing classes. Such a failure would typically be noticed if you were using a build tool. However if you are getting JAR files from someone else, you are dependent on them building properly, and noticing errors. If you suspect this, use tar -tvf to list the contents of the suspect JAR file.

IDE issues: People have reported cases where their IDE gets confused and the compiler in the IDE cannot find a class that exists ... or the reverse situation.

This can happen if the IDE's caches get out of sync with the file system. There are IDE specific ways to fix that.

This could be an IDE bug. For instance @Joel Costigliola describes a scenario where Eclipse does not handle a Maven "test" tree correctly: see this answer.

Redefining system classes: I've seen cases where the compiler complains that substring is an unknown symbol in something like the following

String s = ...
String s1 = s.substring(1);

It turned out that the programmer had created their own version of String and that his version of the class didn't define a substring methods.

Lesson: Don't define your own classes with the same names as common library classes!

Homoglyphs: If you use UTF-8 encoding for your source files, it is possible to have identifiers that look the same, but are in fact different because they contain homoglyphs. See this page for more information.

You can avoid this by restricting yourself to ASCII or Latin-1 as the source file encoding, and using Java \uxxxx escapes for other characters.

1 - If, perchance, you do see this in a runtime exception or error message, then either you have configured your IDE to run code with compilation errors, or your application is generating and compiling code .. at runtime.

2 - The three basic principles of Civil Engineering: water doesn't flow uphill, a plank is stronger on its side, and you can't push on a string.

@Jogi 2016-05-23 07:28:56

I had another situation where this compilation error occured while eclipse didn't see the problem: Two classes with dependencies defined in the respectively other class. In my case I had an enum, implementing an interface, defined in a class where I foolishly already used the enum.

@Andres Stadelmann 2016-05-27 16:42:31

Somewhat similarly to the comment above, when I compile and run my program from Eclipse it works no problem. Compiling it from the console raises a bunch of these "Cannot find symbol" errors often related to last element in an import. I have no idea what is causing this as there is nothing wrong in the code really.

@MC Emperor 2018-08-13 11:14:54

People new to Java are sometimes mixing up array types with their component types, for instance String[] strings = { "hello", "world" }; strings.chatAt(3);.

@avp 2018-08-18 01:45:46

There can be various scenarios as people have mentioned above. A couple of things which have helped me resolve this.

If you are using IntelliJ

File -> 'Invalidate Caches/Restart'

OR

The class being referenced was in another project and that dependency was not added to the Gradle build file of my project. So I added the dependency using

compile project(':anotherProject')

and it worked. HTH!

@GT_hash 2018-06-30 11:09:55

"Can not find " means that , compiler who can't find appropriate variable, method ,class etc...if you got that error massage , first of all you want to find code line where get error massage..And then you will able to find which variable , method or class have not define before using it.After confirmation initialize that variable ,method or class can be used for later require...Consider the following example.

@Stephen C 2017-11-01 13:41:29

"Java has no free() or delete operators, so it has to rely on tracking variable scope to find out when variables are no longer used (together with references to these variables of cause)." - While true, this not relevant. C and C++ have free / delete operators respectively, and yet the equivalent C / C++ code to your examples would be illegal. C and C++ blocks limit the scope of variables just like in Java. In fact, this is true for most "block structured" languages.

@Daniel Pryden 2018-04-03 13:43:56

The better solution for code that assigns a different value on every branch is to use a blank final variable declaration.

@Maria 2016-09-28 14:59:49

I too was getting this error. (for which I googled and I was directed to this page)

Problem: I was calling a static method defined in the class of a project A from a class defined in another project B.
I was getting the following error:

error: cannot find symbol

Solution: I resolved this by first building the project where the method is defined then the project where the method was being called from.

@Joel Costigliola 2016-05-13 10:09:00

One way to get this error in Eclipse :

Define a class A in src/test/java.

Define another class B in src/main/java that uses class A.

Result : Eclipse will compile the code, but maven will give "Cannot find symbol".

Underlying cause : Eclipse is using a combined build path for the main and test trees. Unfortunately, it does not support using different build paths for different parts of an Eclipse project, which is what Maven requires.